Silicon carbide Schottky-barrier devices are high-performance power devices having lower power losses than conventional silicon devices and can operate at higher switching frequencies. SiC presents the advantages of having a high breakdown electric field, high thermal conductivity and high saturated drift velocity of electrons. SiC is a wide bandgap semiconductor and may advantageously be used for manufacturing devices for low-loss power conversion applications, such as rectifiers.
Generally, power rectifier devices may be manufactured from epitaxially grown SiC layers. Epitaxial SiC layers usually present a number of irregularities due to dislocation defects, such as growth pits, hillocks, and growth steps. Such morphology defects may result in regions of electric field concentration increasing the probability of electron tunneling from the Schottky metal into the SiC drift layer, thereby increasing leakage currents at high blocking voltages. High-temperature stages of the manufacturing process of the power rectifier device, such as for example implant anneal, might also result in surface roughening due to diffusion of silicon and carbon along the wafer surface.
The pattern of the electric field concentration depends on the configuration of the irregularities at the SiC surface. A needle-shaped pit, having a relatively narrow width as compared to its depth along the direction of epitaxial growth, may for example cause a high local concentration of the electric field. A shallow pit, having a relatively large lateral extension, may on the other hand result in a smaller extent of electric field concentration. Curvature of radius and depth of the pit, the applied voltage, and the thickness of the doped SiC layer are examples of parameters that may affect the leakage currents of the power rectifier device.
Thus, it would be desirable to provide a power rectifier device, and a corresponding method of manufacturing, wherein a surface of the drift layer has an improved smoothness.